Leadframe-to-plastic lock for IC package

ABSTRACT

Disclosed is a method of making a mold lock for bonding leadframe-to-plastic in an IC package. Steps include providing niches from opposing sides of the leadframe. The opposing niches are arranged such that an aperture and a mechanical key are formed within the leadframe material by the partial intersection of the niches. The key is encapsulated with mold compound to form a lock. An IC package mold lock in a leadframe is also disclosed, the lock having an aperture, a key, and mold compound encapsulating the key. Additionally, an IC package employing the leadframe-to-plastic lock is disclosed.

TECHNICAL FIELD

This application claims priority under 35 USC § 120 of provisionalapplication Ser. No. 10/252,217, filed Sep. 23, 2002 now U.S. Pat No.6,794,738. The present application is a divisional of the aboveidentified application. The invention relates to an IC package mold lockand methods for making the same. More particularly, the inventionrelates to leadframe-to-plastic lock structures and methods for use inIC packages.

BACKGROUND OF THE INVENTION

It is well known to encapsulate IC devices in packages in order toprotect the device and to provide connective leads for coupling theterminals of the IC to the outside world, such as a PC board.

Problems are encountered with packaged IC devices used in the arts bothin the manufacturing stages and in testing and use. Among the problems,some of the most common and debilitating are the separation of layers ofdevices, lead fingers pulling out of the package, and open or shortcircuits caused by separation of materials or the ingress of moisturebetween separated materials. Attempts to improve the bond betweenleadframes and package materials have been made using stamped or etchedvias in the leadframes, which are then filled with encapsulant. Althoughsomewhat resistant to sheering, these efforts have enjoyed limitedsuccess.

Improved leadframe-to-plastic IC package locks would be useful andadvantageous in the arts. Such leadframe locks would provide increasedreistance to sheering and separating forces providing a more securebond.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention, in accordancewith an embodiment thereof, a method of making an IC package mold lockincludes steps of providing a first niche in a leadframe surface andproviding an opposing niche in an opposing leadframe surface. The firstniche and opposing niche partially intersect, defining an aperture inthe leadframe. The niches are arranged such that a key is defined by theintersecting and nonintersecting portions of the niches. The key isencapsulated with mold compound to form a mold lock.

According to one aspect of the invention, an IC package mold lock deviceincludes a leadframe having at least one aperture. The aperture has akey with mold compound disposed in the aperture and encapsulating thekey forming a mold lock.

According to another aspect of the invention, an IC package mold lock isprovided with a key having a first niche in a surface of the leadframeaxially unaligned with a partially intersecting opposing niche in anopposing surface of the leadframe. The niches are of approximatelyidentical same size and shape, the key structure resulting from theirnonalignment.

According to yet another aspect of the invention, an IC package moldlock is provided with a key including a first niche in a surface of theleadframe axially aligned with a partially intersecting opposing nichein an opposing surface of the leadframe. The niches are aligned, but notidentically shaped, the key structure resulting from their shapedifference.

According to still another aspect of the invention, an IC package has aleadframe having a die pad and multiple of lead fingers. A number ofapertures in the leadframe are provided, at least one of which has akey. Mold compound encapsulates the key to form a mold lock.

The invention provides technical advantages including but not limited toproviding an IC package mold lock ensuring a secure mechanical bondbetween the leadframe and encapsulant of an IC package. The inventionmay be used advantageously to provide improved bonds for lead fingers ordie pads in DIP, QFN, SOP, or other semiconductor device packages. Theseand other features, advantages, and benefits of the present inventionwill become apparent to one of ordinary skill in the art upon carefulconsideration of the detailed description of representative embodimentsof the invention in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from considerationof the following detailed description and drawings in which:

FIG. 1 is a top view of an example of an IC leadframe demonstrating moldlocks according to preferred embodiments of the invention;

FIGS. 2A through 2C are sectional views of a portion of a leadframe asshown in the example of FIG. 1 illustrating various stages in apreferred method of making an IC package mold lock according to theinvention;

FIG. 2A is a sectional view of a portion of a leadframe prior to maskingand etching;

FIG. 2B is a sectional view of the portion of a leadframe of FIG. 2Ahaving niches in one surface;

FIG. 2C is a sectional view of the portion of the leadframe of FIG. 1taken along line C—C showing niches in one surface and opposing nichesin an opposing surface;

FIG. 3 is a sectional view of the portion of a leadframe as in theexample of FIG. 2C incorporated into a QFN IC package according to theinvention;

FIG. 4 is a sectional view of the portion of a leadframe as in theexample of FIG. 2C incorporated into a DIP IC package according to theinvention; and

FIG. 5 is a process flow diagram illustrating steps according to oneexample of a preferred method of the invention.

References in the detailed description correspond to like references inthe figures unless otherwise noted. Like numerals refer to like partsthroughout the various figures. Descriptive and directional terms usedin the written description such as top, bottom, left, right, etc., referto the drawings themselves as laid out on the paper and not to physicallimitations of the invention unless specifically noted. The drawings arenot to scale and some features of embodiments shown and discussed aresimplified or exaggerated for illustrating the principles, features, andadvantages of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In general, the invention provides an IC package leadframe mold lock andmethods for making the same. Representatively illustrated in FIG. 1 is atop view of an example of a leadframe 10 according to a preferredembodiment of the invention. The leadframe 10 has a die pad 12 andnumerous lead fingers 14. According to this exemplary embodiment boththe die pad 12 and each of the lead fingers 14 have perforatingapertures 16. It should be understood that the invention mayalternatively be implemented with various combinations of apertures 16in either the die pad 12, some or all of the lead fingers 14, or both,as further described.

As may be seen in FIG. 2C, which is a sectional view of the portion ofthe lead frame 10 of FIG. 1 taken along line C—C, the apertures 16 arelocated within the leadframe material and neither at the top 18 nor atthe bottom 20 surfaces of the leadframe 10. Preferably the apertures areformed by partially etching opposed niches 22, 24 in the leadframesurfaces 18, 20 from either side. Understanding of the leadframe 10shown in FIG. 1 and FIG. 2C and methods of manufacturing the leadframelock of the invention will be enhanced with further reference to FIGS.2A through 2C.

In FIG. 2A, a section of the leadframe 10 is shown. A first surface 18has an opposing surface 20. Using appropriate masking and etchingtechniques known in the arts, first niches 22 as illustrated in thesection view of FIG. 2B are etched into the first surface 18 of theleadframe 10. Opposing niches 24 are also masked and etched into theopposing surface 20 of the leadframe 10 as depicted in FIG. 2C.Preferably, the first niches 22 and opposing niches 24 may be etched atthe same time. The depth of the first niches 22 and opposing niches 24may be varied without departure from the invention as long as anaperture 16 is formed within the leadframe 10. For example, each nichemay extend approximately halfway through the leadframe from eithersurface. Alternatively, one niche may extend approximately one-quarterof the way through and the opposing niche approximately three-quartersthrough the leadframe, or halfway and three-quarters respectively. Theexact configuration of the niches, techniques of their formation, andtheir depth are not crucial to the concept of the invention as long asan aperture 16 is provided by aligning or partially aligning theopposing niches and etching or stamping to depths sufficient to causethe opposing niches to intersect.

Now referring primarily to FIG. 3 a section view of an example of acompleted IC package 26 with a preferred embodiment of a leadframe lock28 of the invention is shown. The leadframe 10 and niches 22, 24 have asemiconductor die 30 attached to the die pad 12 and a wire 32 bonded tothe die 30 and to the lead finger 18 in a manner known in the arts. Thepackage 26 has been completed by the addition of encapsulatingdielectric material 34, typically a form of hard-curing plastic or epoxyresin, generally referred to as plastic or mold compound. The moldcompound 34 encapsulates keys 36 (further discussed below) of theleadframe apertures 16 as shown. It should be appreciated that theniches 22, 24 need not necessarily be completely filled with moldcompound 34, so long as the key 36 is encapsulated, providing amechanical bond.

FIG. 4 illustrates an example of an alternative embodiment of theinvention in a DIP package. The mold lock 28 is provided as described incombination with a DIP package made according to methods known in thearts. The invention may also be used with other packages using ametallic leadframe or die pad, e.g.: SIP, SOIC, SSOP, TSSOP, TVSOP.

It should be understood that the aperture 16 completely perforates theleadframe 10 by the intersection of the niches 22, 24, preferably etchedfrom the opposing leadframe 10 surfaces 18, 20. The aperture 16 itselfmay be any size or shape found desirable for the particularmanufacturing process, tooling, or application. The aperture 16 providesfluid communication for uncured mold compound 34 to flow between theopposing niches 22, 24. Thus, the non-intersecting niche surfaces eachform one or more generally horizontal step 38 between the approximatelyvertical niche walls 40, the horizontal steps 38 being adjacent to theaperture 16. These step surfaces 38 adjoined by an aperture 16 aredenominated “keys” 36 herein, referring to the mechanical key structure36 formed by the junction of the two opposed niches 22, 24, regardlessof shape or size. This mechanical key structure 36, when encapsulated bymold compound 34, form a lead lock 28 providing a secure bond enhancingresistance to sheer and the separation of the layers of the IC package26.

It will be understood by those skilled in the arts that the relativesize and shape of the opposing niches is not an essential feature of theinvention. For example, the niches may be substantially identical insize and shape so long as they are not perfectly aligned along theircentral axes. Again referring to FIG. 1, examples of cylindrical andoval niches of the same size, but offset from one another are shown at42. Alternatively, the niches may be axially aligned, but of differentsize or shape, e.g.; as shown at 44, a relatively larger cylindricalniche may be axially aligned with an opposing relatively smallercylindrical niche, or a cylindrical niche may be used in opposing axialalignment with a rectangular niche 46. Of course, the lock structure mayalternatively be located at an edge portion of the lead finger or diepad as shown at 48. Many alternative niche configurations andarrangements may be used without departure from the invention.

FIG. 5 is a process flow diagram illustrating steps in a preferredmethod of the invention. As shown in steps 100, and 102, a first nicheand opposing second niche are masked at the desired location on theopposing leadframe surfaces. The first niche and second niche areetched, steps 104 and 106 respectively, using processes known in thearts such that the aperture and key structure is formed. The package keystructure is encapsulated 108 to form a secure leadframe mold lock. Ofcourse many variations are possible and some of the steps shown may beperformed simultaneously according to known methods of manufacture. Forexample, the masking steps, or etching steps, may be combined.Additional steps commonly used in the manufacture of IC packages mayalso be used in implementing the invention. For example, a stamping stepmay be substituted for one etching step and associated masking step. Itwill be appreciated by those skilled in the arts that the invention maybe used with various types of device packages, such as DIP, SIP, SOIC,SSOP, TSSOP, TVSOP, and QFN packages, for example.

Thus, the invention provides leadframe locks, IC packages, and methodsused in their construction, providing secure mechanical bonds resistantto separation and sheer. Numerous technical advantages are provided bythe invention, including but not limited to improved package strength,resilience, longevity, manufacturability, and reliability. While theinvention has been described with reference to certain illustrativeembodiments, the description of the methods, systems, and devicesdescribed are not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments as wellas other advantages and embodiments of the invention will be apparent topersons skilled in the art upon reference to the description and claims.

1. A method of making an IC package mold lock comprising the steps of:providing a first niche in a leadframe surface; providing an opposingniche in an opposing leadframe surface, the opposing niche partiallyintersecting with the first niche with a step having an abruptintersection portion such that an aperture in the leadframe is definedby the intersecting portions, and such that a key is defined by thenonintersecting portions; and encapsulating the key with mold compoundto form a mold lock.
 2. The method of claim 1 wherein the encapsulatingstep further comprises filling the first niche, opposing niche, andaperture with mold compound.
 3. The method of claim 1 wherein theproviding steps further comprise the steps of masking and etching theleadframe surfaces.
 4. The method of claim 1 wherein the step ofproviding an opposing niche further comprises the step of providing anopposing niche axially unaligned with a first niche of approximatelyidentical same size and shape.
 5. The method of claim 1 wherein the stepof providing an opposing niche further comprises the step of providingan opposing niche axially aligned with a first niche of nonidenticalsize and shape.
 6. The method of claim 1 wherein the leadframe surfacesfurther comprise lead finger surfaces.
 7. The method of claim 1 whereinthe leadframe surfaces further comprise die pad surfaces.